Device and Method for Information About Plmn Id

1. A mobile station for use in a Radio Access Network (RAN), wherein the RAN is connected to a core network that comprises one or more Public Land Mobile Networks (PLMNs), the mobile station comprising: an interface to communicate with the RAN using Radio Link Control (RLC) data blocks; a processor to: choose one of said PLMNs when accessing a Packet Switched (PS) domain in the RAN; include an identity (ID) of a chosen PLMN in an RLC data block; and include a reserved or pre-defined value in a length indicator field of the RLC data block to inform the RAN that the RLC data block contains the ID of the chosen PLMN, wherein a value of 123 or 62 is used as the reserved or pre-defined value included in the length indicator field.

2. The mobile station of claim 1 , wherein the ID of the chosen PLMN is included after a last Upper Layer PDU of the RLC data block.

3. The mobile station of claim 1 , wherein the mobile station is operable using different RAN modes, and the reserved or pre-defined value used to inform the RAN that the RLC data block contains the ID of the chosen PLMN is different depending on which of the RAN modes is used.

4. The mobile station of claim 3 , wherein the reserved or pre-defined value is different for RAN modes GPRS and EGPRS.

5. A Control Node arranged to be part of a Radio Access Network (RAN), wherein the RAN is connected to a Core Network (CN) that comprises one or more Public Land Mobile Networks (PLMNs), the Control Node comprising: an interface to receive Radio Link Control (RLC) data blocks from a mobile station in a cell in the RAN; a processor to: inspect a length indicator field in an RLC data block; identify a reserved or pre-defined value in the length indicator field, wherein the reserved or pre-defined value indicates that the RLC data block contains an ID of a PLMN selected by the mobile station from the one or more PLMNs, wherein a value of 123 or 62 is identified as the reserved or pre-defined value in the length indicator field; find and extract said ID in the RLC data block; and forward the ID to a node in the RAN or in the CN.

6. The Control Node of claim 5 , wherein said node to which the ID is forwarded to is a Serving GPRS Support Node (SGSN).

7. The Control Node of claim 5 , wherein the processor is further operable to find said ID after a last Upper Layer PDU of the RLC data block in which the ID is included.

8. The Control Node of claim 5 , wherein the Control Node is operable using more than one RAN mode, and the reserved or pre-defined value used to indicate that the RLC data block contains the ID of the selected PLMN is different depending on which RAN mode is used.

9. The Control Node of claim 8 , wherein the reserved or pre-defined value used to indicate that the RLC data block contains the ID of the selected PLMN is different for RAN modes GPRS and EGPRS.

10. The Control Node of claim 5 , wherein the Control Node is a GSM Base Station Controller (BSC) arranged to be part of a Base Station System (BSS).

11. The Control Node of claim 5 , wherein the Control Node is an LTE eNodeB.

12. The Control Node of claim 5 , wherein the Control Node is a WCDMA Radio Network Controller (RNC).

13. A method performed by a mobile station comprising an interface and a processor, wherein the mobile station is connected to a Radio Access Network (RAN) and the RAN is connected to a core network comprising one or more Public Land Mobile Networks (PLMNs), the method comprising: choosing one of said PLMNs when accessing a Packet Switched (PS) domain in the RAN; including an identity (ID) of the chosen PLMN in an RLC data block; including a reserved or pre-defined value in a length indicator field of the RLC data block to inform the RAN that the RLC data block contains the ID of the chosen PLMN, wherein a value of 123 or 62 is used as the reserved or pre-defined value in the length indicator field; and sending the RLC data block to the RAN.

14. The method of claim 13 , wherein the ID of the chosen PLMN is included after a last Upper Layer PDU of the RLC data block.

15. The method of claim 13 , wherein the mobile station is operable using different RAN modes, and the reserved or pre-defined value used to inform the RAN that the RLC data block contains the ID of the chosen PLMN is different depending on which RAN mode is used.

16. The method of claim 15 , wherein the reserved or pre-defined value is different for RAN modes GPRS and EGPRS.

17. A method performed by a Control Node comprising an interface and a processor, wherein the Control Node is part of a Radio Access Network (RAN) and the RAN is connected to a Core Network (CN) comprising one or more Public Land Mobile Networks (PLMNs), the method comprising: receiving Radio Link Control (RLC) data blocks from a mobile station in a cell in the RAN; inspecting a length indicator field in an RLC data block; identifying a reserved or pre-defined value in the length indicator field, wherein the reserved or pre-defined value indicates that the RLC data block contains an ID of a PLMN selected by the mobile station from the one or more PLMNs, wherein a value of 123 or 62 is identified as the reserved or pre-defined value in the length indicator field: finding and extracting said ID in the RLC data block; and forwarding the ID to a node in the RAN or in the CN.

18. The method of claim 17 , wherein said node to which the ID is forwarded to is a Serving GPRS Support Node (SGSN).

19. The method of claim 17 , wherein said ID is found after a last Upper Layer PDU of the RLC data block in which the ID is included.

20. The method of claim 17 , wherein the Control Node is operable using multiple RAN modes, and the reserved or pre-defined value used to indicate that the RLC data block contains the ID of the PLMN selected by the mobile station is different depending on which RAN mode is used.